Process for preparing methylenediphenyl diisocyanate

Process for preparing methylenediphenyl diisocyanate

  • CN 105,503,654 A
  • Filed: 02/27/2009
  • Published: 04/20/2016
  • Est. Priority Date: 03/01/2008
  • Status: Active Application
First Claim
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1. prepare the method for methylenediphenyl diisocyanates, described method comprisesA) aniline and formaldehyde are reacted to generate the diamines of diphenylmethane series and the mixture of polyamine (MDA) under existing as the hydrochloric acid of catalyzer, wherein aniline/formaldehyde reaction is what to carry out at the protonation of <

  • 30%, then uses alkali metal hydroxide to be neutralized at least partly by described hydrochloric acid;

    WhereinA1) will introduce together with raw material, or under the hydrochloric acid as catalyzer exists, form at aniline and formaldehyde the water generated between the reaction period of the diamines of diphenylmethane series and the mixture of polyamine (MDA) and remove at least in part from reaction mixture;

    A2) will at A1) in after the reaction mixture neutralization that formed, obtain the organic phase of the aqueous solution comprising alkali metal chloride and the mixture comprising described diamines and polyamine;

    A3) will A2 be derived from) organic phase separate from aqueous phase, and carry out aftertreatment to obtain the mixture of described diamines and polyamine;

    WithA4) by A3) after the aqueous solution comprising alkali metal chloride that retains with at A1) in any water of removing and with in steps A

         3) in the aqueous phase that obtains in the described organic phase aftertreatment carried out merge;

    Purifying;

    And be fed to electrochemical oxidation C at least in part) in;

    At A4) in purifying before, the described aqueous solution comprising alkali metal chloride is adjusted to pH<

    8B) by the diamines of described diphenylmethane series and the mixture of polyamine and phosgene reaction with the mixture of the vulcabond and polymeric polyisocyanate (MDI) that form diphenylmethane series and hydrogenchloride;

    WhereinC) by A) hydrochloric acid of inner neutralization to comprise the solution isolated in form of alkali metal chloride out, and wherein at least partially described solution be fed directly into electrochemical oxidation subsequently to form chlorine, alkali metal hydroxide and optional hydrogen;

    WithD) use at least partially at C) in formed chlorine be prepared in B) in use phosgene;

    At oxidation C) before, the described aqueous solution comprising alkali metal chloride is adjusted to TOC value <

    200ppm;

    Wherein at C) in electrochemical oxidation carry out as using the alkali chloride electrolysis of ion-exchange membrane, orDescribed electrochemical oxidation carries out with the alkali chloride electrolysis using gas diffusion electrode as negative electrode as using ion-exchange membrane,The alkali metal chloride of the solution wherein containing alkali metal chloride is sodium-chlor, and ion-exchange membrane has the water transport ability of >

    3mol water/mol sodium.

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